On Wed, Oct 10, 2012 at 06:07:34PM +0800, zwu.kernel@gmail.com wrote:

From: Zhi Yong Wu <redacted>

  Add a /sys/kernel/debug/hot_track/<device_name>/ directory for each
volume that contains two files. The first, `inode_data', contains the
heat information for inodes that have been brought into the hot data map
structures. The second, `range_data', contains similar information for
subfile ranges.

Signed-off-by: Zhi Yong Wu <redacted>
---
 fs/hot_tracking.c |  462 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 fs/hot_tracking.h |   43 +++++
 2 files changed, 505 insertions(+), 0 deletions(-)

.....

+static int hot_debugfs_copy(struct debugfs_vol_data *data, char *msg, int len)
+{
+	struct lstring *debugfs_log = data->debugfs_log;
+	uint new_log_alloc_size;
+	char *new_log;
+	static char err_msg[] = "No more memory!\n";
+
+	if (len >= data->log_alloc_size - debugfs_log->len) {

......

+	}
+
+	memcpy(debugfs_log->str + debugfs_log->len, data->log_work_buff, len);
+	debugfs_log->len += (unsigned long) len;
+
+	return len;
+}
+
+/* Returns the number of bytes written to the log. */
+static int hot_debugfs_log(struct debugfs_vol_data *data, const char *fmt, ...)
+{
+	struct lstring *debugfs_log = data->debugfs_log;
+	va_list args;
+	int len;
+	static char trunc_msg[] =
+			"The next message has been truncated.\n";
+
+	if (debugfs_log->str == NULL)
+		return -1;
+
+	spin_lock(&data->log_lock);
+
+	va_start(args, fmt);
+	len = vsnprintf(data->log_work_buff,
+			sizeof(data->log_work_buff), fmt, args);
+	va_end(args);
+
+	if (len >= sizeof(data->log_work_buff)) {
+		hot_debugfs_copy(data, trunc_msg, sizeof(trunc_msg));
+	}
+
+	len = hot_debugfs_copy(data, data->log_work_buff, len);
+	spin_unlock(&data->log_lock);
+
+	return len;
+}

Aren't you just recreating seq_printf() here? i.e. can't you replace
all this complexity with generic seq_file/seq_operations constructs?

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com